The real answer is star navigation at night and interial + sun guided during the day. Phone hardware is perfectly capable but ITAR says otherwise. There's a reason why every legal GPS receiver shuts down after altitude or speed limits are exceeded. Too easy to make weapons that fly in your window from hundreds of miles away, basically
From mynameisvlad link given below[1] the restrictions are to prevent intercontinental missile navigation not regular missile navigation. The official limits are a speed (1,000 knots) and an altitude (18,000 m), but many manufactures do an "or" test instead.
"In GPS technology, the term "COCOM Limits" also refers to a limit placed on GPS tracking devices that disables tracking when the device calculates that it is moving faster than 1,000 knots (1,900 km/h; 1,200 mph) at an altitude higher than 18,000 m (59,000 ft).[2] This was intended to prevent the use of GPS in intercontinental ballistic missile-like applications.
Some manufacturers apply this limit only when both speed and altitude limits are reached, while other manufacturers disable tracking when either limit is reached. In the latter case, this causes some devices to refuse to operate in very high altitude balloons."
They don't need to. There is a great many of more cost-effective ways of causing havoc, and even if they really wanted to use GPS-guided missiles, it's probably a better bet to build slower missiles with consumer hardware, but build a lot of them - missile interceptors are very expensive. If a DIY $1k missile needs to be shot down by $1M Patriot, they'll be doing lots of damage with a couple of them, without even hitting anything.
That's not true at all. You can use a $20 SDR card to receive GPS signals and and then can decode them on any commodity laptop, or a small computer like a raspberry pi.
Receiving the signals is only a part of the problem, and even getting a "fix" isn't all that hard. Maintaining an accurate fix, and at the same time refining away previous errors, on a fast moving vehicle, is a dark art.
Software architectures are the limiting factor here.
Every app on your phone cares about "Where am I now", but no app wants to know "Where was I 5 seconds ago, but with more accuracy than you knew when I last asked".
Neither android not iPhone have an API to allow GPS hardware to refine the accuracy of historic position locations.
Possible maybe but unusual. 99% of ham is narrowband, GPS is spread across a megahertz. Somebody goofed and made a TV tuner chip that could be used as an SDR at that sample rate, and I'm sure the powers that be arent happy.
Any sensitive Spectrum Analyser or SDR can see the bump in the spectrum caused by the GPS Signals. And quite a few amateurs have built homebrew GPS receivers.
Or they can buy a little GPS module and use the data stream for a huge range of projects.
Most modern digital Ham communication methods require a 10MHz feed from a GPS module to maintain sufficient time and frequency accuracy.
Too late to edit so replying to myself. I was mostly wrong. The GPS limits are much higher than I thought, and accuracy of INS is too low, although I still think that limit is artificial.
The limits are higher altitude and faster speed then you've ever been. If the Concorde was around you would see it firsthand. Weapons would be worthless against first world defences at airliner height and speed. Gps receivers shut down on weather balloons regularly, it's a known issue
The limits are real, encoded in public law. I don't understand how you could possibly disagree with me on this point
The reason your GPS receiver does not work on a plane is likely because it's processing algorithms aren't tuned for those speeds. The popular Ublox NEO-6M for example needs to be explicitly switched to "airborne" mode.
The fact that you are enclosed in a faraday cage also isn't helping, but they make planes from plastic now, so this shouldn't always be the case.
Unfortunately many cheap GPS chips use the (incorrect) or definition, not and. It was a pain to find one that works above 59000ft but very slow speed for a weather balloon project some years ago.
I like using a NSF funded mobile app "Flyover Country" [1] to identify features in the landscape when I fly. You can download the maps and data for you flight path a head of time and then use it in airplane mode on the plane. GPS works fine (by the window) and the app locates your position on the map.
